E/CN.4/2000/4 page 9 allow doctors to treat persons believed to be opposed to a government, or fails to provide immunization against the community’s major infectious diseases, on grounds such as national security or the preservation of public order, has the burden of justifying such serious measures in relation to each of the elements identified in article 4. Such restrictions must be in accordance with the law, including international human rights standards, compatible with the nature of the rights protected by the Covenant, in the interest of legitimate aims pursued, and strictly necessary for the promotion of the general welfare in a democratic society. 29. In line with article 5.1, such limitations must be proportional, i.e. the least restrictive alternative must be adopted where several types of limitations are available. Even where such limitations on grounds of protecting public health are basically permitted, they should be of limited duration and subject to review. II. STATES PARTIES’ OBLIGATIONS General legal obligations 30. While the Covenant provides for progressive realization and acknowledges the constraints due to the limits of available resources, it also imposes on States parties various obligations which are of immediate effect. States parties have immediate obligations in relation to the right to health, such as the guarantee that the right will be exercised without discrimination of any kind (art. 2.2) and the obligation to take steps (art. 2.1) towards the full realization of article 12. Such steps must be deliberate, concrete and targeted towards the full realization of the right to health.20 31. The progressive realization of the right to health over a period of time should not be interpreted as depriving States parties’ obligations of all meaningful content. Rather, progressive realization means that States parties have a specific and continuing obligation to move as expeditiously and effectively as possible towards the full realization of article 12.21 32. As with all other rights in the Covenant, there is a strong presumption that retrogressive measures taken in relation to the right to health are not permissible. If any deliberately retrogressive measures are taken, the State party has the burden of proving that they have been introduced after the most careful consideration of all alternatives and that they are duly justified by reference to the totality of the rights provided for in the Covenant in the context of the full use of the State party’s maximum available resources.22 33. The right to health, like all human rights, imposes three types or levels of obligations on States parties: the obligations to respect, protect and fulfil. In turn, the obligation to fulfil contains obligations to facilitate, provide and promote.23 The obligation to respect requires States to refrain from interfering directly or indirectly with the enjoyment of the right to health. The obligation to protect requires States to take measures that prevent third parties from interfering with article 12 guarantees. Finally, the obligation to fulfil requires States to adopt appropriate legislative, administrative, budgetary, judicial, promotional and other measures towards the full realization of the right to health.